The humidity in the computer room has changed from about 50% down to 35% Relative Humidity (RH). What influence does this have on Electrostatic Discharge (ESD)?

A decrease in relative humidity (RH) makes the air a more effective electrical insulator. Moisture (water vapor) in the air provides a conductive path that helps to dissipate static charges from surfaces before they can accumulate to dangerous levels. When the air becomes drier, as in the drop from 50% to 35% RH, this conductive path is diminished. Consequently, static charges build up more easily on personnel and equipment, leading to a significantly higher potential voltage. This increased voltage potential directly translates to higher and more frequent Electrostatic Discharge (ESD) events, which can damage sensitive electronic components within the data center.

A. Temperature stability does not negate the direct and significant impact that a change in relative humidity has on ESD potential.
B. This is factually incorrect. Relative humidity is one of the most critical environmental factors influencing the generation and accumulation of electrostatic charge.
D. This states the opposite of the actual physical principle. Lowering the humidity increases the potential for ESD, it does not decrease it.

1. ASHRAE TC 9.9. (2021). Thermal Guidelines for Data Processing Environments (5th ed.). In Chapter 3, "IT Equipment Design and Environmental Specifications," the guidelines establish a minimum moisture level (dew point temperature) specifically to mitigate the risk of electrostatic discharge. The text explains that operating below this lower moisture limit increases the propensity for ESD events. A drop in RH at a constant temperature corresponds to a drop in moisture level.

2. Schneider Electric. (2012). Humidification Strategies for Data Centers and Network Rooms. White Paper 58, Rev 2. On page 3, under the section "Why Humidify?", it states: "When relative humidity drops below approximately 40%, static electricity becomes a concern... The lower the RH, the more readily a static charge can build up. This charge can then discharge into a sensitive piece of electronic equipment, causing damage." This directly confirms that a drop from 50% to 35% RH increases ESD levels.

3. ESD Association. (2016). ESD TR20.20-2016 - Handbook for the Development of an Electrostatic Discharge Control Program. Section 5.1.3, "Effect of Humidity," provides data showing the dramatic effect of RH on static generation. For example, walking across a vinyl tile floor can generate 12,000 volts at 10-20% RH, but only 1,500 volts at 65-90% RH. This illustrates the principle that lower humidity leads to higher static voltage levels.